【英文】BBC纪录片行星地球Planet Earth 1-5
Midsummer on the tundra and the sun does not set （固定搭配：sunset 日落） . At these latitudes the sun's rays （ ray和light的区别：light表示光，既可以是physical层面的，也可以是mental层面的，如思想之光等，而ray更偏向于科学表达的射线，可以看到光的直射的路径的那种，如X-ray ） are glancing and not enough of their energy reaches the ground to enable trees to grow. You'll need to travel 500 miles south from here before that is possible. These stunted shrubs mark the tree line - the beginning of the boreal （北方的） forest - the taiga（泰加林，针叶林带）.
The needle-shaped leaves of the conifers （针叶树） are virtually inedible （不可食用） so this forest supports very little animal life. It's a silent place where the snow is unmarked by footprints. In the Arctic winter snow forms a continuous blanket across the land. But as spring creeps up from the south the taiga is unveiled. This vast forest circling the globe contains a third of all the trees on Earth and produces so much oxygen it changes the composition of the atmosphere.
